Test-plug for protective apparatus.



No. 783,995. PATENTED FEB. 28, 1905.

'F. B. COOK. TEST PLUG FOR PROTECTIVE APPARATUS.

APPLICATION FILED APRAll, 1904.

)Iilnesses: .Ezverzior:

Patented February 28, 1905.

PATENT OFFICE.

FRANK B. COOL, OF CHICAGO, ILLINOIS.

TEST-PLUG FOR PROTECTIVE APPARATUS- SPECIFIGATION forming part of Letters Patent N 0. 783,995, dated February 28, 1905.

Original application filed December 4, 1903, Serial No. 183,733, Divided and this application filed April 11, 1904. Serial No. 202,653.-

To It LU/00711, zit 'nur/ concern:

Be it known that l, FRANK B. Coon, a citizen of the United States, residing at Chicago, in the county of Cook and State of Illinois, have invented new and useful Improvements in Test-Plugs for Protective Apparatus, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

This application is a division of my application for patent on protective apparatus, Serial No. 183,733, iiled December 4, 1903.

My invention relates to a test-pl ug to be used in connection with testing apparatus and electrical protective apparatus such as is used for protecting telephone-circuits from harmful electric currents, my object being to provide a convenient arrangement of such a test-plug and protective apparatus whereby the different circuits through the said apparatus may be readily and etiiciently tested without removing any of the protective devices from their respective circuits.

The arrangement of protective apparatus as herein shown is for supporting and operating two classes of current-protecti ve devices namely, protective devices which protectelectrical circuits and apparatus from high-tension electrical discharges, such as lightning, and protective devices which protect against small sneak currents. The high-tension electric discharges are guarded against by means of lightning-arresters, preferably consisting of carbon blocks with interposed (lielectrics and the sneak currents are guarded against by means of heat-coils or thermal arresters. This protective apparatus com prises spring-simports provided with suitable contacts and arranged for holding the lightningarresters an: heat-coils, the said spring-supports being suitably mounted on a plate which is preferably a part of the iron supporting-frame and eonductively connected to earth. When this apparatus is used in connection with telephone systems, the said springs are used as'terminals for the line, switchboard, and alarm-circuits. When a thermal arrester operates, it throws a ground on certain springs of the combination, and

thereby connects the objectionable current to earth. I

The test-pl ug comprising this invention consists of a number of spring contact members, preferably arranged in pairs insulated from each other and adapted to cooperate with respective springs of the protective apparatus. These spring contact members are conductively connected with respective contacts of a switch which is adapted to connect the said members of the test-plug with a test instrument, and thereby allow different circuits through the protective apparatus to be tested when the test-plug is connected with the said protective apparatus. The spring contact mem bers of the test-plug are suitably mounted on an insulating-block which gives a convenient arrangement for handling.

1 will more particularly describe my invention by reference to the accompanying drawings. illustrating same, in which is Figure 1 is a side view of the test-plug. Fig. 2 is a side view of the protective apparatus with which the test-plug cooperates. Fig. 3 is an edge view of the test-plug and protective apparatus shown in Figs. 1 and 2, and Fig. 4 is a view showing the testplug eonductively connected with the protective apparatus for testing and the test-circuits and testing apparatus.

Like characters refer to like parts in the several figures.

The metal plate /12. is preferably a part of the iron framework supporting the strips of protective zwparatus or a part of a distributing-board through which the telephone-lines pass on their way to a central-station switchboard, and it is preferably connected to earth. It may be a part of any apparatus on which protective devices are mounted. The protective devices and springs are mountedin pairs upon plate m and are preferably arranged so that the two devices forming a pair are mounted one on either side of this plate m and opposite to each other. As the two protective devices forming a pair are similar to each other, 1 will describe in detail one only of the pair.

The conductor-strip r is secured to one edge of plate 1/1 and is provided with small projections r 1 thereon between which projections the carbon lightnmg-arrester (7 is placed.

Springs 0, f, 7, (7, c, and 7) are all mounted fiatwise on one side of plate 1/1 by two doubleended bolts s and If. The bolts .v andz pass through suitable holes in the plate m and are insulated from m by suitable insulating sleeves and washers )7, preferably of hard rubber. Spring 0 is mounted next to plate m. but insulated therefrom, and is provided with a contact at its free end adapted to make contact with the ground-strip 1' when the spring is depressed and with a hole therein through which an insulating-pin 7 passes and rests against the plate m. This spring is used for closing an alarmcircuit. Spring f is mounted next to spring 0, but insulated therefrom, and extends past the forward edge of plate 111., so as to form a support for the lightning-arrester a. Spring f is made narrow at its free end, so as to fit in a groove in one of the carbon blocks of the lightning-arrester a. which is inserted between springf and ground-strip v' and held in place by the tension in spring f and the projections 1 on strip '1'. Spring 7" is also provided with a hole therein through which a contact-point 7: passes when the heatcoil operates and with another hole therein through which the insulatingpin 7 passes. The insulating-pin 7 is provided with a shoulder near its inner end adapted to hold spring 6 out of contact with spring 7. Spring 77/ is mounted next to spring f, so as to make electrical contact therewith, and is provided with ears g near its free end adapted to firmly hold a heat-coil therebetween. Spring (7 is also provided with a contact-point 7', adapted to pass through a hole in spring 7" and make contact with spring a when the heat-coil operates and with a hole therein through which the insulating-pin 7 freely passes. Spring (7 is mounted against spring (7, serving to stiffen the latter, and is provided with a hole therein through which the insulating-pin 7 freely Spring 0 is mounted next to spring passes. d, but insulated therefrom, is provided with a curved portion at its free end adapted to engage a toothed member Z of the heat-coil and with a hole therein through which the insulating-pin 7 passes, the tension in spring 0 being against a shoulder near the outer end of pin '7, which supports spring a in a rigid position. Spring 7) is mounted next to spring 0, but insulated therefrom at its fixed end, and is provided with contact-points 0 0 at its free end, which rest against spring 0 and make contact therewith and which serve to prevent lateral displacement of a test-plug inserted therebetween. Spring 6 is split at 7), so as to allow contact-points 6* 7f to make contact with spring 0 independently of each other. 1 Springs 7) and c are turned over at their free ends to enable the springs of the test-plug to be readily inserted between them.

In Fig. 2 1 preferably show the heat-coils in a set position, as they are intended to be in this position when the test-plug is used for testing the circuits through the protective apparatus. The principal circuits may be tested, however, when the heat-coils are in an operated position, as shown upon the right of Fig. 4.

On the right-hand side of' Figs. 2 and 4 spring 7) is conductively secured to bolt 7; by a nut, but insulated from bolts. Terminal 7) is mounted on bolts 8 and 1, being insulated from bolt .xand conductively secured to bolt t. On the left-hand side of Figs. 2 and t springs f, (7, and (7 are conductively secured to bolt by a nut, but insulated from bolt 7'. Terminal f is also mounted on bolts x and if, being in- (Z, and f on the opposite side of plate "m from f through the agency of bolt s.

This arrangement puts the line-terminalsf and f on one side of the plate m and the switchboardterminals 7) and 7) on the other side of plate m.

The test-plug consists of an insulating-block w, preferably of hard rubber, on each end of which is mounted a series of springs, the

said springs being insulated from each other and arranged so that the springs v, 11.1, and on one end of the block 11: form pan-s with respective correspomling springs :1 and 1 on the other end of block w. Springs v are curved and loosely held to block w at their respective free ends by pins as" of, respectively, so as to allow springs or r to give when the test-plug is connected with the protectorsprings. Metal strips y/ y are mounted adjacent to springs 1 respectively, and are provided with turned ends ;1 f, respectively, which act as stops for the test-plug when it is connected with the sprii'igs of the protective apparatus.

\Vhen the test-plug is connected with the protector-springs for testing, as shown in Fig. 4, springs 1/ y engage springs 7) 7), respectively, springs :11 :1 engage sprn'igs o c, re-

spectively, and springs w engage the carbon blocks a, a, respectively. On either side of plate m springs 1/1 and y of the test-plug are forced between springs c and 7) of the protective apparatus, thus forcing springs c and 7) apart and breaking the electrical connection between them. Projections rest against springs 7) 7), respectively, and springs w w rest against the ends of springs ff, respectively, all forming stops for the test-plug. Springs j g are connected to conductors l5 and 16,

respectively, springs :11 :1 are connected to conductors 13 and 14, respectively, and springs 2: r are connected to conductors 11 and 12, respectively. Conductor 15 is connected to switch-contact 5, conductor 13 to contact 3 and 8, conductor 11 to contacts 1 and 7 conductor 12 to contacts 9 and 2, conductor 1 1 to contacts 4 and 10, and conductor 16 to contact 6. The switch 2 is adapted to connect the test instrument in circuit with contacts 1 and 2. 3 and 1, 5 and 6, 7 and 8, or 9 and 10, as desired. This affords a simple means for testing the switchboard, the line through the heat-coils, the line direct, or either heat-coil. separately.

The circuits to be tested are as follows: first, from contacts 1 and 2, through conductors l1 and 12, springs 02 4), carbon blocks a a, springs ff, bolt a, terminal and the telephone-line which is connected to terminals ,2 and f second, from contacts 3 and 4,

through conductors 13 and 14, springs a springs c c, toothed members v1 and their respective heat-coils, springs (Z (Z, springs ff, bolt 8, terminal f and the telephone-line which is connected to terminals f and f third. from contacts 5 and 6, through conductors 15 and 16, springs 3/ springs 11 0, bolt 6, terminal 6 and the switchboardcir cuit which is connected to terminals and];; fourth, from contact 7, through conductor 11, spring c, (on the left of Fig. &) carbon block a, spring f, spring (Z, ears g and the heat-coil contained therebetween, toothed member 1', spring 0, spring in, and conductor 13 to contact 8; fifth, from contact 9, through conductor 12, spring 4;, (on the right of Fig. 4,) carbon block a, spring f, spring (Z, ears 4 and the heat-coil contained therebetween, toothed member i, spring 0, spring as, and conductor 14 to contact 10. While I have traced out metallic circuits for the line and switchboard testing, it is evident that grounded return or common return circuits may be equally tested. In testing between contacts 7 and 8 or between contacts 9 and 10 the heat-coils and their contacts with their connecting-springs are tested as in actual service.

\Vhile I have described particular details of construction in this invention, I do not wish to limit myself to such exact details. The form of protective apparatus and heat-coils as herein shown may be greatly varied. hat I desire to hereinafter claim is the combination of a test-plug with protective apparatus and testing apparatus to accomplish the desired results and general methods embodied in the above description.

Having thus described my invention, what 1 claim as new, and desire to secure by Letters Patent, is

1. In apparatus of the class specified, the combination of a thermal protector, a normally closed switch associated with the protector and electrically connected therewith, a test-plug provided with contact members insulated from each other and adapted to cooperate with the said switch to open same and make connection for testing the apparatus, the said plug also being adapted to be connected with a testing instrument, substantially as described.

2. The combination with a thermal protector comprising means for controlling a circuit under abnormal current conditions, and a spring-switch electrically connected therewith; of a test-plug adapted to be connected with said switch to test a circuit, and also with a suitable testing instrument.

3. The combination of a test-plug for protective apparatus, comprising a pair of contact members insulated t'r in each other, and suitably mounted, and a pair of protectors suitably mounted, the said contact members cooperating with like parts of the pair of pro tectors for the purpose of testing.

a. The combination with a pair of thermal protectors and pairs of normally closed switchcontacts in circuit with the respective protectors, of a test-plug having pairs of contacts insulated from each other, the pairs of contacts of the test-plug being adapted to be inserted between the respective pairs of normally closed switch-contacts of the protectors, and thereby open the said normally closed switch-contacts, the said plug being adapted to be connected with a testing instrument, and means for preventing lateral displacement of the test-plug.

5. The combination with a thermal protector and a pair of flat metallic switch-contacts conductively connected therewith, one of the said pair of contacts being in the nature of a spring adapted to normally bear against the other, of a test-plug provided with a pair of flat contacts separated by interposed insulation and adapted to be inserted between the said normally closed contacts of the protector, the said plug being adapted to be connected with a testing instrument, and means at each side of the said switch-contacts of the protector to maintain the plug in place between the said contacts.

6. The combination with a pair of thermal protectors and pairs of flat metallic switchcontacts conductively connected with the respective protectors, one of the said switchcontacts of each pair being in the nature of a spring adapted to normally bear against the other switch-contacts, respectively, of a testplug provided with pairs of flat contacts, each pair being separated by interposed insulation and adapted to be inserted between the said normally closed contacts of either protector, the said plug being adapted to be connected with a testing instrun'ient, and means at each side of the said switch-contacts of the protectors to maintain the test-plug in place between the said pairs of switch-contacts.

7. The combination with a thermal protector comprising means for controlling a circuit and operable upon the passage of an abnormally large current therethrough, and a switch-socket electrically connected there with, of a test-plug adapted to be inserted in TOO IIO

said socket to test a circuit, the said plug being adapted to be connected with a suitable testing instrument, and means included by the switch-socket tor preveiiting lateral displacement of the plug.

8. The combination with thermal protectors comprisii'ig means tor controlling respective circuits and operable upon the passage of abnormally large currents through the pro tectors, and a switch-socket for each protector and electric: lly connected therewith, ot' a test-plug adapted to be inserted in the said sockets to test a circuit, the said plug being adapted to be connected with a suitable testing instrul'ncnt, and means included by the switch-sockets for preventing lateral displacement of the plug.

9. The combination of a test-plug for protective apparatus, comprising a pair ol springconnectors insulated from each other and suit ably mounted, and a pair of similar protectors suitably mounted, the spring-connectors cooperating with like parts of the pair ol pro tectors, for the purpose of testin 10. The con'ibination ot' a testaglug for protective apparatus, comprising pairs of springconnectors suitably mounted and insulated from each other, and protective apparatus comprising a duplicate set of protectors, the pairs of spring-connectors ot the test-plug cooperating with respective pairs of like parts of the protective apparatus, for the purpose of testing, substantially as described.

11. The combination of a testplug for protective al'n'iaratus, comprising pairs of switchcontacts insulated from each other, the contacts of each pair being mounted upon opposite ends ot a block of insulation, protective apparatus comprising a duplicate set of protectors, a switch, and a test instrument adapt ed to be thrown in circuit with certain switchcontacts of the test-plug which are adapted to cooperate with respective springs ol the duplicate protective apparatus, for the purpose of testing different circuits through the protective apparatus, substantially as described.

12. The combination with protective apparatus comprising duplicate sets of springs mounted on opposite sides o't aground-plate, of a test-plug for such a1 paratus, comprising pairs of connecting-springs adapted to coopi erate with the duplicate sets of springs of the protective apparatus, the said springs of the test-plug being insulated from each other, and the springs of each pair being mounted upon opposite faces of a block of insulation, a test instrument, and a switch adapted to connect the test lnstrument in clrcuit with certain sprlngs of the test-plug, tor the purpose ol testing di'tl'erent circuits through the protectl ive amiaratus, substantially as described.

13. The combination of a test-plug for pro tective a 'iparatus, provided with switch-coni tacts adapted to cooperate with said apparatus, a ground-plate, springs for each side of the l ground-plate and mounted flatwise thereon, said springs being adapted to cooperate with said test-plug switch-contacts; and being lineterminals, switchboard-terminals and protectl ive-device terminals, and a switch and test instrument adapted to co perate with the testplug, whereby, when the switch-contacts ol the test-plug are engaged with the springs ol the protective apparatus, the line-circuits, switchboard-circuits and protective-device circuits may be tested independently ol each other, substantially as described.

1%. The combination in a test-plug to be used in connection with [n'otective apparatus, of a block of insulation, pairs of springs, the springs 01 each pair being mounted on opposite ends of the said block, each spring being insulated trom all ol the other springs, the sprin s of one pair being provided with respective stops to limit the insertion ol the test-plug into the protective apparatus, and means for connecting the pairs 0t springs in respective test-circuits, substantially as described.

15. In a test-plug and socket-switch arrangement for testing protective apparatus, the combination ot a grouml-plate, a ground strip secured to one edge thereof, a pair olsuperposed springs on each side 01 the groundplate mounted 'l'latwise thereon and insulated therefrom and from ach other,onespringot each pair being held stationary by a suitable support, the other spring ol each pair being movable, a protective device for each pair of springs and held therebetwimn, a third spring for each pair, mounted llatwise on the ground- 1 plate between the latter and the respective i inner springs of the said pairs, the said third springs being conductively secured to the respective inner springs of the said pairs, lightning-arresters inserted between the respective third springs and the ground-strip, a Fourth spring for each pair, mounted llatwise on the ground-plate, outside of the respective outer springs of the said pairs, the said l'ourth springs being insulated from the groundplate and from the other spriligs, at their lixed ends, and making contact with the respective outer springs of the said pairs at their tree ends, the said test-plug being pro vided with individual springs adapted to engage the respective said fourth springs. the respective outer springs of the said pairs, and the respective said third springs and lightning-arresters, the said fourth springs being switchboaI'd-terminals, the said third springs beingline-terminals, and the said outersprings of the pairs being dead at their mounting, a projection on each outer spring of the testplug, adapted to limit the insertion ol the l l l test-plug into the protective apparatus, a switch provided with contacts to which the respective springs ol the testplug are connected, and a testinstrument connected in circuit with the said switch, all coi'iperating,

whereby, when the springs of the test-plug l of contact members in respective test-circuits,

are engaged with the springs of the protective apparatus, the switchboard-cireuits may be tested independently of the line-circuits, the line-circuits may be tested direct, independently of the switchboard-circuits, the line-circuits may be tested through the said protective devices, independently of the switch boardcircuits, and the protective devices themselves, together with the contacts of their connectirig-springs, may be tested separately, independently of the switehboard-circuits or line-circuits, substantially as described.

16. The combination in a testing arrangement for protective apparatus, of a thermal protector comprising normally closed switchcontacts, a heat-concentrating member and means operated thereby for opening the circuit, the said switch-contacts and heat-concentrating member being adapted to be connected in series in a circuit; and a test-plug having contacts adapted to be inserted between the said normally closed switch-contacts, said plug being adapted to be connected with a testing instrument; the protector having means at each side of the said switchcontacts to maintain the plug in place.

17. The combination in a testing arrangement for protective apparatus, of a thermal protector comprising a pair of flat metallic switch-contacts whereot' one is in the nature of a spring adapted to normally bear against the other, a heat-concentrating member and means operated thereby for opening a circuit, said heat-concentrating member and metallic contacts being in series; and a plug provided with a pair of flat contacts separated by interposed insulation, said plug-contacts being adapted to be thrust between said normally closed metallic contacts of the thermal protector, and said plug being adapted to be connected with a testing instrument; the protector having means at each side of the said switch-contacts to maintain the plug in place between the contacts.

18. The combination with a thermal protector comprising means for opening a circuit and operable upon the passage of an abnormally large current through the device and a socket switch electrically connected therewith; of a test-plug adapted to be inserted in said socket to test a circuit, the said plug being adapted to be connected with a suitable testing instrument, and means included by the socket-switch for preventing lateral displacement or the plug.

19. The combination in a test-plug to be used in connection with electrical protective apparatus, of a piece of insulation pairs of contact members, the members of each pair being mounted on opposite faces of the said insulation, each contact member being insulated from the others, suitable stops to limit the insertion of the test-plug into the protective apparatus, and means for connecting the pairs substantially as described.

20. r'kpparatus comprising a pair of thermal protectors for electrical circuits, normally closed socket-switches electrically connected with the respective protectors, and a testingplug adapted to be inserted in both of the socket-switches at the same time, for testing purposes.

21. In electrical protective apparatus, the combination with a ground-plate, of doubleended bolts passing therethrough and insulated therefrom and from each other, a pair of superposed springs mounted flatwise on the said plate by the said bolts but insulated from the said plate and lrom each other, a protective device adapted to be held in a state of stress by the said springs, a third spring outside of the pair of springs, mounted flatwise on the said plate by the said bolts, and insulated from the other said springs at its mounting, and contact-points near the free end of the said third spring and adapted to bear against the outer spring of the pair to form a normally closed socket-switch adapted to reeeive a test-plug, the said contacts preventing lateral displacel'nent oi the test-plug, one of the said bolts conduetively connecting one spring of the pair with a cormection-terminal on the opposite side of the ground-plate, substantially as described.

22. In electrical protective apparatus, the combination with a ground-plate, 01 doubleended bolts passing therethrough and insulated threfrom and from each other, a pair of superposed springs mounted fiatwise on the said plate by the said bolts but insulated from the said plate and from each other, a protective device adapted to be held in astate of stress by the said springs and conduetively connected from one to the other, athird spring outside of the pair of springs, mounted flaiwise on the said plate by the said bolts and insulated from the other said springs at its mounting, and contact-points near the free end of the said third spring and adapted to form a normally closed socket-switch adapted to receive a test-plug, the said contacts preventing lateral displacement of the test-plug, one of the said bolts conduetively connecting the said third spring with a conneetion-ter minal on the opposite side of the ground-plate,

substantially as described.

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spective said pairs, and insulated from the l other said springs at their mounting, and contact-points near the respective free ends of the said third springs and adapted to form normally closed socket-switches with the re spective outer springs of the pairs, the said socket-switches being adapted to receive a test-plug, the said contact-points preventing lateral displacement of the test-plug, one of the said bolts conductively connecting the inner spring of one pair with a connectionter minal on the opposite side of the ground-plate, the other said bolt conductively connecting one said third spring with aconnection-terminal on the opposite side of the ground-plate, substantially as described.

24. In protective apparatus for electric circuits, the combination of a ground-plate, a pair of superposed springs mounted on one side thereof but insulated therefrom and from each other, a thermal protector held in a state of stress between the said springs, a third spring mounted on the said plate and adapted to form a normally closed socket-switch with one spring of the pair, the said socket-switch being adapted to receive a test-plug, and means for connecting the said third spring, the socket-switch, the thermal protector, and one spring of the pair, in a series circuit.

25. In an electrical protector, a socketswitch having normally closed contacts adapted to receive a co1mecting-plug and to prevent lateral displacen'ient thereof, an excess-current-operable device connected in circuit with the said switch. and means for engaging the said device and tending to operate same.

26. An electrical protector comprising a pair of flat springs forming a normally closed socket-switch adapted to receive a connectingplug, metallic contacts included by the socketswitch and adapted to prevent lateral displacement of the plug, a thermal cut-out connected in circuit with the socket-switch, and spring means for engaging the cut-out and tending to turn same upon its support.

27. In apparatus of the class specified, a plurality of normally closed socket-switches provided with means for receiving a connecting-plug of a testing instrument, metallic contacts in the switches for preventing lateral displacement of said plug, and electrical protectors adapted to be connected in circuit with the respective switches.

28. In protective apparatus for electric cirl cults, the combination of a ground-plate, a 1

pair of superposed springs for each side of the ground-plate and mounted thereon, but insulated therefrom and from each other, a thermal protector for each pair and held in a state of stress between the springs of the pair, a third spring for each pair mounted on the said plate and adapted to form normally closed socketswitches with respective springs of the pairs, the said socket-switches being adapted to receive a test-plug, and means for connecting the said third springs, the socket-switches, the thermal protectors, and one spring of each pair, in a series circuit.

29. In an electrical protector, socketswitches provided with means for receiving a connecting-plug, metallic contacts in each of the socket-switches for preventing lateral displacement of the plug, cxcess-current-operable devices connected in circuit with the socket-switches, and means for engaging the said devices to operate same.

30. An electrical protector comprising pairs of flat springs forming normally closed socketswitches adapted to receive a connecting-plu g, metallic contacts included by the socketswitches and adapted to prevent lateral displacement of the plug, thermal cutouts connected in circuit with the socket-switches, and spring means for engaging the cut-outs and tending to turn same upon their supports.

31. In an electrical protector, a socketswitch provided with means for receiving a connecting-plug, means for preventing lateral displacement of the plug, a separable conductor associated with said socket-switch and connected in circuit therewith, a heat-producing means adapted to cause the separable conductor to operate,and a spring normally under tension and engaging said separable conductor.

0.4. In a device for protecting electrical cir cnits against abnormally large currents, a thermal cut-out, asocket-switch provided with means for receiving a connecting-plug and connected in series with the cut-out, means in the switch for preventing lateral displacement of the plug, and means for operating the cut out to control a circuit.

33. In a device for protecting electrical circuits against excessive current, a heat-concentrating member, a spring socket-switch connected in series therewith, means in the switch for preventing lateral displacement of a testing-plug, and means for automatically opening the circuit through the heat-concentrating member under abnormal current conditions.

3A. In electrical protective apparatus, socket-switches provided with means for re ceiving a testing-plug and for preventing lateral displacement of the plug, a separable conductor for each socket-switch and conductively connected therewith, and a spring member for each separable conductor, normally under tension and engaging the latter to operate same.

In apparatus of the class specified, socket-switch and lightning-arrestersprovid ed with means for receiving a tcstplug and for preventing lateral displacement thereof, thermal protectors associated withthe socketswitches, and suitable mounting and contactsprings for the thermal protectors and light- 1'1ing-arresters.

36. In apparatus for protecting electrical circuits against abnormally large currents,

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thermal protectors, socket-switches connected l with means for preventing lateral displacein circuit With the thermal protectors and p rovided with means for receiving a testing-plug and for preventing lateral displacement of the plug, a suitable support to which the Whole is mounted, and means for controlling a circuit when a thermal protector operates.

37. In apparatus for protecting electrical circuits against excessive current, excess-current-operable devices, spring socket-switches connected in series therewith and provided ment of a connecting-plug, and means whereby the operation of an excess-current-mgerable device controls a circuit.

In Witness thereof I hereunto subscribe my name this QeLth day of March, A. l). 1904:.

FRANK B. COOK.

\Vitnesses:

J NO. F. TOMPKINS, FREDERICK R. PARKER. 

